Emission tomography technology such as PET (Positron Emission Tomography) and SPECT (Single-Photon Emission Computed Tomography) has been extensively used in many fields such as medical diagnosis, pathology and pharmacology research, drug development and the like.
For example, the PET uses the annihilation effect which occurs between the positron produced by isotope decay and negatron within human body, to obtain the distribution information of the isotope within human body through injecting radioactive tracer into human body (e.g., compounds with positron isotope labeling) and detecting gamma photons generated from the annihilation effect by the detector. The reconstruction of the distribution information could be carried out with a computer to get the three-dimensional tomographic image of the labeled compound distribution within the human body.
One of the most important parameters of the medical emission tomography system (e.g., whole-body PET system) is the detection sensitivity, which represents the ability of the system acquiring effective signal data, and is critical to the spatial resolution of the image reconstructed by the system. Clinically, the relatively high detection sensitivity contributes to the reduction of the dosage of the radioactive tracer, the shortening of the imaging time and the improvement of the SNR (Signal to Noise Ratio). The detection sensitivity of the emission tomography system depends on the geometrical efficiency and the detection efficiency to the inherent coincidence event. The geometrical efficiency depends on the space angle surrounded by the detector modules.
Currently, the emission tomography system still adopts a traditional design scheme. That is, each of the detector modules has substantially the same performance and size, and the detector modules are permanently fixed after the emission tomography system is built, which restricts the detection sensitivity in some cases. For example, the detection sensitivity would decrease when the emission tomography system suitable for the whole human body is applied to a child or a small animal.